Quarried material is often processed by means of crushing plant, for the production of aggregate, for example. There are various known forms of crushing plant for the comminution of rock material and the like, one of which is referred to as a jaw crusher.
GB2387342 describes a known jaw crusher of the kind having a fixed jaw and a swing jaw disposed between opposing side walls of the jaw crusher, wherein the swing jaw is movable relative to the fixed jaw, for generating impelling forces to crush material present in a crushing chamber defined by between the two jaws. The jaw crusher includes a cross beam which extends through apertures in the opposing side walls, and a toggle plate is provided between a rear face of the swing jaw and the cross beam. An hydraulic cylinder is mounted in each of said side wall apertures, for applying a load to cross beam, which is transmitted to the swing jaw via the toggle plate.
A shim pack consisting of a plurality of removable shim plates is provided in each side wall aperture, between the front face of the cross beam and an end surface of the respective aperture, for setting and adjusting the normal working clearance between the lower end of the swing jaw and the fixed jaw.
Crushing forces generated during movement of the swing jaw are passed through the toggle plate against the cross beam and back to the hydraulic cylinders. However, the hydraulic cylinders are pre-pressurized to a predetermined value, for example 400 bar, against an end surface of the respective side wall apertures, through the cross beam and the shim pack, and thereby provide a pre-loaded reaction to the forces generated during movement of the swing jaw.
This provides a substantially compact design of jaw crusher, which has particular advantage for use as mobile plant.
If pressure generated during the crushing cycle becomes excessive, for example in an overload situation where an uncrushable object is present in the crushing chamber, the load applied to the cross beam via the toggle plate will exceed the pre-load pressure of the hydraulic cylinders. To address this, a relief valve is provided in an hydraulic circuit to the cylinders. This allows fluid under pressure to be released from the hydraulic cylinders, allowing the respective cylinder piston to be pushed backwards, to enable the swing jaw to move away from the fixed jaw and thereby to allow the crushing chamber to be cleared safely.
In order to adjust the spacing between the lower ends of the jaws, it is first necessary to release the pressure from the cylinder arrangements, to enable the pistons to retract. This relieves the load on the cross beam and allows safe removal of the shim packs.
The present invention provides a more adaptable jaw crusher arrangement.